1. Field of the Invention
The present invention relates to a receiver-driven layered multicast rate control protocol and more particularly to a protocol for enabling and disabling layers utilizing IGMP (Internet Group Management Protocol) extensions.
2. Description of the Related Art
While there are evolving techniques for the provision of IP (Internet Protocol) quality of service (QoS) arrangements, there is in need for architectures to provide streaming services in the widely deployed IP best-effort networks. Rate control is a crucial element in such architectures for streaming multimedia data to resolve congested network states and to exploit spare bandwidth in the network to insure the best transmission quality. This is of particular importance when considering multicast scenarios with heterogeneous bandwidth capabilities along a transmission path from a sender to a group of receivers.
The layered encoding approach provides a transmission of different layers which are combined into a stream or flow of information. Within a local subsystem of a network, an adaptation scheme is applied to enable the transmission of appropriate layers, if the bandwidth is available, and to disable the transmission of the layers in the case of network congestion. With this approach, the available bandwidth can be adapted locally to support heterogeneous environments.
The RLM (Receiver-driven Layered Multicast) technique was originally proposed in the article entitled: Receiver-driven Layered Multicast, Proceedings of ACM SIGCOMM, August 1996, by Stephen McCanne, Van Jacobson, and Martin Vetterli. This article is incorporated by reference herein in its entirety.
As noted in the article, a transmission and rate control scheme for multicast environments is proposed using layered encoding of the information flows. That is, information, such as a video stream, is transmitted in different layers which are then combined at the receivers. Usually, there is a base layer providing a minimum quality along with extension layers which are used to improve the quality of the received stream.
For an implementation of the RLM scheme, IGMP (Internet Group Management Protocol) may be used. IGMP is a recommended standard of the IETF (Internet Engineering Task Force) and is defined in RFC 2236, entitled: Internet Group Management Protocol Version 2, November 1997 by W. Fenner. This standard is incorporated by reference herein in its entirety. Furthermore, related standard RFC 1112, entitled: Host Extensions for IP Multicasting, August 1989, by S. Deering, specifies the extensions required of a host implementation of the IP needed to support multicasting and this related standard is also incorporated by reference herein in its entirety.
As noted in this standard, a layer is disabled in the case of congestion by leaving the appropriate multicast group and a layer is added by joining the group locally. For that, the appropriate IGMP operations are invoked (join/leave) at the local upstream multicast router. However, the use of IGMP operations for the enable/disable operations add significant delay and complexity. For example, when leaving the group, the upstream multicast router sends a query to the local group to determine whether there are other group members left. The router waits for a defined time interval until the transmission and this multicast group is stopped. Furthermore, when joining the group, the transmission can be immediately continued only if the multicast spanning tree is still valid. If not, the entire spanning tree build operation of the appropriate routing protocol must be issued again which adds a significant delay and a large overhead to the system due to the number of operations which must be performed.
These IGMP-specific latencies are known as join/leave latencies and restrict the usage of the protocol due to its poor responsiveness. Furthermore, the RLM protocol and its derivatives use specific rate adjustment procedures to apply in the IGMP join/leave operations.
The following references, noted below, disclose the use of the specific rate adjustment procedures noted above and are all incorporated by reference herein in their entirety:
The article entitled: Thin Streams: An Architecture for Multicasting Layered Video, Proceedings of 7th International Workshop on Network and Operating System Support for Digital Audio and Video (NOSSDAV), May 1997, by Linda Wu, Rosen Sharma, and Brian Smith.
The article entitled: TCP-like Congestion Control for Layered Multicast Data Transfer, Proceedings of INFOCOM, April 1998, by Lorenzo Vicisano, Luigi Rizzo, and Jon Crowcroft.
The article entitled: TEAR: TCP Emulation at Receivers—Flow Control for Multimedia Streaming, April 2000, by Injong Rhee, Volkan Ozdemir, and Yung Yi.
The article entitled: PLM: Fast Convergence for Cumulative Layered Multicast Transmission Schemes, Proceedings of ACM SIGMETRICS, June 2000, by A. Legout and E. W. Biersack.